The present invention relates to an alternator installed on an automotive vehicle or a truck (i.e. automotive alternating-current generator).
Many automotive vehicles employ a slant nose style to reduce the aerodynamic resistance and improve traveling performance. The automotive engines are equipped with various devices. The number of such engine accessories is recently increasing. On the other hand, the passenger compartment of an automotive vehicle needs to be wide or high enough to provide a satisfactory and comfortable space for the driver and other passengers. From these factors, the available space for an alternator in the engine room is very narrow. In other words, the ambient temperature of an automotive alternator tends to be high. Meanwhile, the power generation ability of each automotive alternator must be high to provide sufficient electric power to various electric devices installed on the vehicle. Thus, the heat generation of an automotive alternator is increasing. From the above circumstances, it is necessary to improve the cooling properties of a rectifying unit that includes a rectifying element, preferably at a lower cost, because the rectifying element causes a large temperature increase compared with other constituent parts of the automotive alternator.
The rectifying unit of an automotive alternator includes a positive-electrode side heat radiation fin to which a positive-electrode side rectifying element is fixed and a negative-electrode side heat radiation fin to which a negative-electrode side rectifying element is fixed. The positive-electrode side heat radiation fin and the negative-electrode side heat radiation fin are laminated in an axial direction via a terminal platform embedding connecting terminals. Furthermore, the negative-electrode side heat radiation fin is directly fixed to an end surface of a frame by means of a screw, as disclosed in the Japanese Patent Application Laid-open No. 2000-253625 (pages 3-6 and FIG. 1-13) corresponding to the U.S. Pat. No. 6,198,188.
However, according to the above-described conventional rectifying unit, a large amount of heat will transfer from a stator via the frame to the negative-electrode side heat radiation fin because the negative-electrode side heat radiation fin is directly fixed to the end surface of the frame by means of screws. The cooling air entering from its rear cover tends to be blocked by the positive-electrode side heat radiation fin. Thus, almost all of the introduced cooling air cannot be effectively used for cooling the negative-electrode side heat radiation fin. Accordingly, the negative-electrode side heat radiation fin has poor cooling properties.